Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
In terms of architecture, the terminal end of a cased well often extends into an open-hole section. Thus, completions hardware may be fairly complex and of uniquely configured parts, depending on the particular location and function to be served. For example, in addition to the noted casing, the hardware may include gravel packing, sleeves, screens and other equipment particularly suited for installation in the open-hole section at the end of the well. However, hardware supporting zonal or formation isolation may be located above the open-hole section. Further, certain features such as chemical injection lines may traverse both cased and open-hole well regions. Once more, such complex architecture may need to remain flexible enough in terms of design and installation sequence so as to account for perforating, fracturing, gravel packing and a host of other applications that may be employed in completing the well.
With the above factors in mind, the sequence of hardware installation, following drilling and casing of the well, may begin with gravel packing directed at the open-hole productive region of the well. In terms of hardware delivery for a corresponding lower completion, this may include the installation of screen equipment, a gravel pack packer, a frac sleeve and other features at this productive interface. The result is a cased well that now terminates at a lower completion having at least a temporary degree of fluid control.
This temporary fluid control may consist of no more than employing frac sleeves closed over the formation interface at the lower completion. Thus, an intermediate completion, targeting a more secure form of well control may be installed. That is, once the lower completion is installed, a second trip into the well dedicated to the installation of a formation isolation valve with sealing architecture running to the lower completion may be installed. Thus, a more reliable and permanent form of control may be provided. Once more, this second intermediate completion may include the delivery of a polished bore receptacle, or “PBR”, assembly. As such, a receiving platform is provided for subsequent installation of production tubing and other hardware of the upper completion.
The intermediate completion is delivered by way of work string that not only is used for installation, but also achieves proper isolation during delivery. For example, the string delivers the intermediate completion with the formation isolation valve open, lands out and is then withdrawn in a manner that closes the valve before the string leaves sealed engagement with the PBR there above. As a result, fluid control over the lower completion is tightly maintained from the moment of installation of the intermediate completion.
With the intermediate completion fully installed and a means of permanent control now available over the lower completion, the upper completion may be installed as noted above. That is, a third trip into the well for delivery of and installation of production tubing, internal electric submersible pump (ESP), intelligent completion consisting of flow control valves and other equipment may now safely proceed. This equipment may be safely landed out at the PBR and installed without undue concern over maintaining fluid control over the underlying lower completion.
Unfortunately, the installation of the intermediate completion in order to provide a secure and reliable platform for the subsequent upper completion installation is an extremely costly undertaking. For example, depending on the overall depth of the well, the intermediate installation may take two days or more and consume millions of dollars in terms of equipment, rig-up and other dedicated time-related costs. Furthermore, the presence of an intermediate completion means that the number of equipment mating applications is doubled. That is, rather than simply mating an upper completion to a lower completion, an intermediate completion is mated to the lower followed by the mating of the upper completion to the intermediate. This doesn't just add time, it doubles the likelihood of mismatching or damaging the completions hardware during installation.
The possibility of loss of well control may be dramatically expensive if not catastrophic. Thus, in spite of the drawbacks associated with the intermediate completion as noted above, it remains preferable to have one installed. That is, as opposed to sole reliance on less secure well control features, such as closed sleeves of the lower completion, the installation of an intermediate completion generally remains the best available option for attaining a reliably installed upper completion.